Presently, after various DC-DC converters or inverters power off, electric energy stored in a direct current bus capacitor needs to be discharged via an additional discharging circuit, otherwise, the waiting time for discharging is very long, thus leading to safety concern.
In a conventional discharging circuit, a discharging resistor with a high resistance is directly connected in parallel to a bus capacitor. After powered off, the bus capacitor discharges continuously via the discharging resistor. However, such a continuous discharge also occurs during operating of a system, which results in shortcomings of energy loss and low efficiency. In addition, for the discharging resistor connected in parallel to the high-voltage bus, insulation, heat dissipation and installation methods need to be taken into account.
In another conventional discharging circuit, a switching unit, a discharging unit connected to the bus capacitor via the switching unit, and a controlling unit connected to the switching unit are included. The controlling unit is configured to control, in a power-off state, the switching unit to be turned on to cause the discharging unit and the bus capacitor to form a discharging loop, and control, in a power-on state, the switching unit to be turned off. When this type of discharging circuit is applied in a high-voltage DC-DC converter, two of the discharging circuits are required, resulting a high hardware cost, and a large structural space being occupied. Therefore, a barrier to a design trend of small volume and high density is formed for a modular DC-DC converter.
In view of the above problems, it is urgent to provide a discharging method of a bus capacitor without the need for an additional discharging circuit.